Agricultural irrigation mediates climatic effects and density dependence in population dynamics of Chinese striped hamster in North China Plain

A global evaluation of the associations between long-term dynamics of seed falls and rodents

One classic system of pulsed resource and animal population is mast seeding and population dynamics of seed-eating rodents in forests. However, we still lack an understanding of the global patterns regarding the contributions of seed falls to rodent outbreaks or population dynamics. We analyzed a global dataset of coupled long-term time series of seed abundances and rodent populations from published literature, including 66 and 89 time series (156 rodent-seed pairs from 37 studies) for rodent and seed abundances, respectively. We found only half of the examined rodent populations showed statistically significant coincidence between rodent outbreak and mast-seeding years. Over all the coupled time series, seed abundance was found to positively correlate with rodent abundance with a one-year lag, and the relative importance of seed abundance was much lower than that of density dependence in affecting rodent population growth rates. We also found the relative importance of seed abundance decreased, but that of rodent density dependence increased with the latitude of study. For the first time, our work provides a global pattern on the associations between seed falls and rodent population dynamics mostly in mid- and high-latitude forests, and highlights the necessity of more long-term studies on this subject in more forest ecosystems.

Effects of Plant Coverage on the Abundance of Adult Mosquitos at an Urban Park

People who take a walk in urban parks, including or adjacent to a water body such as a river, a pond, or a lake, usually suffer from mosquito bites in summer and early autumn. The insects can negatively affect the health and mood of these visitors. Prior studies about the effects of landscape composition on the abundance of mosquitos have usually taken stepwise multiple linear regression protocols to look for the landscape variables that can significantly affect the abundance of mosquitos. However, those studies have largely overlooked the nonlinear effects of landscape plants on the abundance of mosquitos. In the present study, we compared the multiple linear regression (MLR) with the generalized additive model (GAM) based on the trapped mosquito abundance data obtained by using photo-catalytic CO₂-baited lamps placed at the Xuanwu Lake Park, a representative subtropical urban scenic spot. We measured the coverage of trees, shrubs, forbs, proportion of hard paving, proportion of water body, and coverage of aquatic plants within a distance of 5 m from each lamp's location. We found that MLR and GAM both detected the significant influences of the coverage of terrestrial plants on the abundance of mosquitos, but GAM provided a better fit to the observations by relaxing the limitation of the linear relationship hypothesis by MLR. The coverage of trees, shrubs, and forbs accounted for 55.2% of deviance, and the coverage of shrubs had the greatest contribution rate among the three predictors, accounting for 22.6% of the deviance. The addition of the interaction between the coverage of trees and that of shrubs largely enhanced the goodness of fit, and it increased the explained deviance of the GAM from 55.2% to 65.7%. The information in this work can be valuable for the planning and design of landscape plants to reduce the abundance of mosquitos at special urban scenic points.

Impacts of Dietary Protein and Niacin Deficiency on Reproduction Performance, Body Growth, and Gut Microbiota of Female Hamsters (Tscherskia triton) and Their Offspring

Food resources are vital for animals to survive, and gut microbiota play an essential role in transferring nutritional materials into functional metabolites for hosts. Although the fact that diet affects host microbiota is well known, its impacts on offspring remain unclear. In this study, we assessed the effects of low-protein and niacin-deficient diets on reproduction performance, body growth, and gut microbiota of greater long-tailed hamsters (Tscherskia triton) under laboratory conditions. We found that maternal low-protein diet (not niacin deficiency) had a significant negative effect on reproduction performance of female hamsters (longer mating latency with males and smaller litter size) and body growth (lower body weight) of both female hamsters and their offspring. Both protein- and niacin-deficient diets showed significant maternal effects on the microbial community in the offspring. A maternal low-protein diet (not niacin deficiency) significantly reduced the abundance of major bacterial taxa producing short-chain fatty acids, increased the abundance of probiotic taxa, and altered microbial function in the offspring. The negative effects of maternal nutritional deficiency on gut microbiota are more pronounced in the protein group than the niacin group and in offspring more than in female hamsters. Our results suggest that a low-protein diet could alter gut microbiota in animals, which may result in negative impacts on their fitness. It is necessary to conduct further analysis to reveal the roles of nutrition, as well as its interaction with gut microbes, in affecting fitness of greater long-tailed hamsters under field conditions. IMPORTANCE Gut microbes are known to be essential for hosts to digest food and absorb nutrients. Currently, it is still unclear how maternal nutrient deficiency affects the fitness of animals by its effect on gut microbes. Here, we evaluated the effects of protein- and niacin-deficient diets on mating behavior, reproduction, body growth, and gut microbiota of both mothers and offspring of the greater long-tailed hamster (Tscherskia triton) under laboratory conditions. We found that a low-protein diet significantly reduced maternal reproduction performance and body growth of both mothers and their offspring. Both protein and niacin deficiencies showed significant maternal effects on the microbial community of the offspring. Our results hint that nutritional deficiency may be a potential factor in causing the observed sustained population decline of the greater long-tailed hamsters due to intensified monoculture in the North China Plain, and this needs further field investigation.

Sustained population decline of rodents is linked to accelerated climate warming and human disturbance

Background

During the past three decades, sustained population decline or disappearance of cycles in small rodents have been observed. Both anthropogenic disturbance and climate warming are likely to be potential drivers of population decline, but quantitative analysis on their distinct effects is still lacking.

Results

Using time series monitoring of 115 populations (80 populations from 18 known rodent species, 35 mixed populations from unknown species) from 1980 in China (spanning 20–33 yrs), we analyzed association of human disturbances and climate warming with population dynamics of these rodent species. We found 54 of 115 populations showed a decreasing trend since 1980, and 16 of 115 showed an increasing trend. Human disturbances and climate warming showed significant positive associations with the population declines of most rodent species, and the population declines were more pronounced in habitats with more intensified human disturbance such as cities and farmlands or in high-latitude regions which experienced more increase of temperature.

Conclusions

Our results indicate that the large-scale sustained population decline of small mammals in various ecosystems driven by the rapid increase of both climate warming and human disturbance is likely a signal of ecosystem dysfunction or transition. There is an urgent need to assess the risks of accelerated climate warming and human disturbance imposes on our ecosystems.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-022-02056-z.

Factors influencing range contraction of a rodent herbivore in a steppe grassland over the past decades

Climate warming and human disturbance are known to be key drivers in causing range contraction of many species, but quantitative assessment on their distinctive and interactive effects on local disappearance is still rare.

In this study, we examined the association of climate warming and human disturbance stressors with local disappearance probability of Brandt's voles (Lasiopodomys brandtii) in a steppe grassland in northern China.

We used logistic generalized additive models to quantify the relationship between local disappearance probability of Brandt's voles and environmental variables. The year following the last observation year was used to estimate the disappearance threshold of Brandt's voles. We projected the distribution change of Brandt's voles under future climate warming scenarios.

We found climate warming attributed to local disappearance and range contraction for southern populations of Brandt's voles from 1971 to 2020. Human stressors and high vegetation coverage increased the probability of local disappearance of voles in years of abundant precipitation. The southern boundary retreated northward at a speed of 99.0 km per decade with the temperature rise of 0.36°C. The disappearance threshold of maximum air temperature of Brandt's voles in the warmest month (27.50 ± 1.61°C) was similar to the lower critical temperature of its thermal neutral zone.

Our study suggests that the rapid climate change over the past decades contributed to the range contraction of its southern boundary of this keystone species in the steppe grassland of China. It is necessary to take actions to preserve the isolated populations of Brandt's voles from the effects of accelerated climate change and human disturbance.

Organochlorine Pesticide Ban Facilitated Reproductive Recovery of Chinese Striped Hamsters

Organochlorine pesticides (OCPs) have been used worldwide on an enormous scale over the last century but are banned globally due to environmental persistence and ecotoxicity in recent decades. The long-term effects of OCP ban for agricultural use in China since 1983 on the reproductive health of small terrestrial mammals have never been evaluated in the field. We examined the residue dynamics of OCPs and the reproductive performance of Chinese striped hamsters (Cricetulus barabensis) in North China Plain during 1983-2010 and concluded that the exposure levels of OCPs in hamsters drastically decreased from 2900 ± 740 to 25.2 ± 6.88 ng/g with an average half-life of 5.08 yrs, coinciding with the observed reproductive recovery of hamsters. The population-based reproductive performance of hamsters was significantly and negatively associated with OCP exposure levels after adjusting the contributions from climate and population density factors, indicating that the ban of OCPs has facilitated the reproductive recovery of hamsters by up to 81% contribution. Our findings suggest that the OCP ban is effective to restore reproduction of small terrestrial mammals. Integration of population biology and environmental science is essential to assess the impacts of persistent organic pollutants on ecological safety and biodiversity loss under accelerated global change.

Effects of density dependence and climatic factors on population dynamics of Cricetulus barabensis: a 25-year field study

Rodents often act as keystone species in communities and play important roles in shaping structures and functions of many ecosystems. Understanding the underlying mechanisms of population fluctuation in rodents is therefore of great interest. Using the data from a 25-year field survey carried out in Inner Mongolia, China, we explored the effects of density dependence, local climatic factors, and a large-scale climatic perturbation (El Niño–Southern Oscillation) on the population dynamics of the striped hamster (Cricetulus barabensis), a rodent widely distributed in northern China. We detected a strong negative density-dependent effect on the population dynamics of C. barabensis. Rainfall had a significant positive effect on population change with a 1-year lag. The pregnancy rate of C. barabensis was negatively affected by the annual mean temperature in the current year, but positively associated with the population density in the current year and the annual Southern Oscillation Index in the previous year. Moving-window analyses suggested that, with a window length of 12 years, there was a significant interaction between rainfall and density dependence, with increasing rainfall alleviating the negative effect of density dependence. As C. barabensis often causes agricultural damage and can transmit zoonotic diseases to human beings, our results also have implications for pest and disease control.

Effects of tannins on population dynamics of sympatric seed-eating rodents: the potential role of gut tannin-degrading bacteria

Chemical compounds in seeds exert negative and even lethal effects on seed-consuming animals. Tannin-degrading bacteria in the guts of small mammals have been associated with the ability to digest seeds high in tannins. At the population level, it is not known if tannins influence rodent species differently according to the composition of their gut microbiota. Here, we test the hypothesis that sympatric tree species with different tannins exert contrasting effects on population fluctuations of seed-eating rodents. We collected a 10-year dataset of seed crops and rodent population sizes and sequenced 16S rRNA of gut microbes. The abundance of Apodemus peninsulae was not correlated with seed crop of either high-tannin Quercus mongolica or low-tannin Corylus mandshurica, but positively correlated with their total seed crops. Abundance of Tamias sibiricus was negatively correlated with seed crop of Q. mongolica but positively correlated with C. mandshurica. Body masses of A. peninsulae and T. sibiricus decreased when given high-tannin food; however, only the survival of T. sibiricus was reduced. The abundance of microbial genus Lactobacillus exhibiting potential tannin-degrading activity was significantly higher in A. peninsulae than in T. sibiricus. Our results suggest that masting tree species with different tannin concentrations may differentially influence population fluctuations of seed predators hosting different gut microbial communities. Although the conclusion is based on just correlational analysis of a short time-series, seeds with different chemical composition may influence rodent populations differently. Future work should examine these questions further to understand the complex interactions among seeds, gut microbes, and animal populations.

Interannual cycles of Hantaan virus outbreaks at the human-animal interface in Central China are controlled by temperature and rainfall

Hantavirus, a rodent-borne zoonotic pathogen, has a global distribution with 200,000 human infections diagnosed annually. In recent decades, repeated outbreaks of hantavirus infections have been reported in Eurasia and America. These outbreaks have led to public concern and an interest in understanding the underlying biological mechanisms. Here, we propose a climate-animal-Hantaan virus (HTNV) infection model to address this issue, using a unique dataset spanning a 54-y period (1960-2013). This dataset comes from Central China, a focal point for natural HTNV infection, and includes both field surveillance and an epidemiological record. We reveal that the 8-y cycle of HTNV outbreaks is driven by the confluence of the cyclic dynamics of striped field mouse (Apodemus agrarius) populations and climate variability, at both seasonal and interannual cycles. Two climatic variables play key roles in the ecology of the HTNV system: temperature and rainfall. These variables account for the dynamics in the host reservoir system and markedly affect both the rate of transmission and the potential risk of outbreaks. Our results suggest that outbreaks of HTNV infection occur only when climatic conditions are favorable for both rodent population growth and virus transmission. These findings improve our understanding of how climate drives the periodic reemergence of zoonotic disease outbreaks over long timescales.

The seesaw effect of winter temperature change on the recruitment of cotton bollworms Helicoverpa armigera through mismatched phenology

Knowing how climate change affects the population dynamics of insect pests is critical for the future of integrated pest management. Rising winter temperatures from global warming can drive increases in outbreaks of some agricultural pests. In contrast, here we propose an alternative hypothesis that both extremely cold and warm winters can mismatch the timing between the eclosion of overwintering pests and the flowering of key host plants. As host plants normally need higher effective cumulative temperatures for flowering than insects need for eclosion, changes in flowering time will be less dramatic than changes in eclosion time, leading to a mismatch of phenology on either side of the optimal winter temperature. We term this the "seesaw effect." Using a long-term dataset of the Old World cotton bollworm Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) in northern China, we tested this seesaw hypothesis by running a generalized additive model for the effects of the third generation moth in the preceding year, the winter air temperature, the number of winter days below a critical temperature and cumulative precipitation during winter on the demography of the overwintering moth. Results confirmed the existence of the seesaw effect of winter temperature change on overwintering populations. Pest management should therefore consider the indirect effect of changing crop phenology (whether due to greenhouse cultivation or to climate change) on pest outbreaks. As arthropods from mid- and high latitudes are actually living in a cooler thermal environment than their physiological optimum in contrast to species from lower latitudes, the effects of rising winter temperatures on the population dynamics of arthropods in the different latitudinal zones should be considered separately. The seesaw effect makes it more difficult to predict the average long-term population dynamics of insect pests at high latitudes due to the potential sharp changes in annual growth rates from fluctuating minimum winter temperatures.

Weakening density dependence from climate change and agricultural intensification triggers pest outbreaks: a 37-year observation of cotton bollworms

Understanding drivers of population fluctuation, especially for agricultural pests, is central to the provision of agro-ecosystem services. Here, we examine the role of endogenous density dependence and exogenous factors of climate and human activity in regulating the 37-year population dynamics of an important agricultural insect pest, the cotton bollworm (Helicoverpa armigera), in North China from 1975 to 2011. Quantitative time-series analysis provided strong evidence explaining long-term population dynamics of the cotton bollworm and its driving factors. Rising temperature and declining rainfall exacerbated the effect of agricultural intensification on continuously weakening the negative density dependence in regulating the population dynamics of cotton bollworms. Consequently, ongoing climate change and agricultural intensification unleashed the tightly regulated pest population and triggered the regional outbreak of H. armigera in 1992. Although the negative density dependence can effectively regulate the population change rate to fluctuate around zero at stable equilibrium levels before and after outbreak in the 1992, the population equilibrium jumped to a higher density level with apparently larger amplitudes after the outbreak. The results highlight the possibility for exogenous factors to induce pest outbreaks and alter the population regulating mechanism of negative density dependence and, thus, the stable equilibrium of the pest population, often to a higher level, posing considerable risks to the provision of agro-ecosystem services and regional food security. Efficient and timely measures of pest management in the era of Anthropocene should target the strengthening and revival of weakening density dependence caused by climate change and human activities.

Temporal change in body mass of two sympatric hamster species and implications for population dynamics

Shifting of body size distributions of animals has been a long-time focus in population ecology, but the underlying mechanism of density-dependent changes in body size and its implications for population dynamics of animals are largely unknown. In this 26-year study, we investigated intrinsic and extrinsic factors affecting body mass of the Chinese striped hamster (Cricetulus barabensis Pallas, 1773) and the greater long-tailed hamster (Tscherskia triton de Winton, 1899) in the Northern China Plain. We proposed three hypotheses to explain body mass shifts in the two hamster species: growth, survival, and reproduction hypotheses. Our results showed that mean and maximum body masses of both hamster species were positively correlated with population density, and that this density-dependent change in body mass is more likely to be caused by a change in mortality rates, not by a change in growth rates or reproduction rates. The sustained decline of body mass during the study period was probably caused by increased mortality owing to an increase in the area of agricultural irrigation. Our results suggest that, under the condition of lacking survival and growth data, the maximum body mass (which represents survival rate), minimum body mass (which represents growth rate), and mean body mass are very useful criteria in revealing intrinsic and extrinsic effects on population dynamics and the underlying mechanisms.